This invention refers to a process and an equipment for marking an article of foam material whenever some irregularity has been ascertained during its manufacturing process.
The foam material articles are usually manufactured by means of moulds formed by two shells having inner cavities which, when both shells forming the mould are joined, define the final shape in which the article is to be formed. When the mould is open, a prefixed amount of reactive mixture is introduced in the cavity of the lower shell of the mould, then the upper shell of the mould is immediately superimposed. The reactive mixture starts quickly a foaming and cross-linking reaction, increases its volume up to fill in entirely the inner cavity of both shells of the mould, and then it sets by assuming a hardness depending upon the composition and quantity of the reactive mixture introduced in the mould. After a sufficient period of time, the mould may be opened and the produced article is removed from the mould. All these operations are effected in sequence and at the prescribed time by an automatic equipment. The components of the reactive mixture, once they are mixed together, react very quickly, and therefore the mixture has to be formed at the very moment it is introduced in the mould, by suitably metering its components which arrive through separate ducts to a metering head. In order to obtain an article having the desired features, it is required that the ratio of the components arrived to the metering head and the amount of the released mixture correspond, within certain tolerance limits, to prefixed values. By means of an automatic control equipment these operational parameters may be surveyed, processed and compared with the imposed limit values, and the control equipment may issue a warning signal each time for any reason a discrepancy between the detected values and the admitted fields of the imposed parameters is noticed. Whenever a warning signal is issued, an operator must mark the mould in whose respect the irregular operative parameters have been detected. When at a later time the produced article is extracted from the marked mould, it should be rejected or conveyed, separately from the correctly produced articles, to a particular examination in order to ascertain whether its characteristics may be accepted or it should be rejected. Nevertheless, the need for operators to mark a mould whenever an operative irregularity has been noticed and to shift away the article to a different destination as soon as it is extracted from a marked mould hinders the automatic production, imposes the requirement of personnel, otherwise not necessary, and moreover it introduces the possibility of human errors.
In order to preserve the automatic production it would be desirable to be able to mark not the mould, wherein an irregularly produced article is setting, but the article itself, whereby it could be separated from the regularly produced articles during any further step of the article treatment. This, however, has not been possible so far, because during the short period of time between the detection of the irregularity in the operative parameters and the immediately subsequent moment in which the mould is closed, the article has not yet been formed, and therefore it cannot receive any kind of marking.